Those that refrain from allowing a younger sibling to get married prior to an older sibling mention the verse from Lavan, "Lo Yaiose Kain BimiKomeinu Losais Hatziyira Lifnei HaBechira, In our locale we do not marry off the younger child prior to the older one". Are there any other sources for this Minhag? Is there an age that you say "at this point we stop waiting"? (sources please)

The real question is "Why are we we following minhag hamakom of a bunch of idolaters in aram naharayim?"
–
YitzchakJun 12 '11 at 22:25

Well if you read the response, it mentions also the Bnos Tzelafchad.
–
Gershon GoldJun 13 '11 at 1:37

@Yitzchak: also, the fact that the Torah mentions this custom (and doesn't find it objectionable) indicates that it has validity.
–
AlexJun 14 '11 at 3:43

1

@Alex, Although the Torah does not find it objectionable, it is clear that Yaakov was perfectly content to marry the younger sister before the older was married. Do we see Lavan's excuse as more legitimate than what Yaakov was ready to do in practice?
–
jakeJun 16 '11 at 18:10

@jake: well, we see that Yaakov waited seven years to marry Rachel; that might be in keeping with one of the Lubavitcher Rebbe's points (quoted in Menachem's answer) - that this was, among other things, to give time for Leah to find a shidduch too. If that's the case, then that would imply that Yaakov agreed with this principle too, just that he didn't consider it a showstopper.
–
AlexJun 17 '11 at 0:57

Why must the younger sister/brother ask for forgiveness? Did they do something terrible to them?
–
ImrayApr 26 '13 at 1:03

@Imray: I think it's making sure that there are no ill feelings, that the older sister is OK with it.
–
MenachemApr 26 '13 at 1:10

I understand that, but I wouldn't call it "forgiveness". More like seeking their blessing.
–
ImrayApr 26 '13 at 1:20

@Imray: From the link: "if the older sister will forgive [her younger sister] with complete forgiveness, this matter [of her getting married first] has been permitted [by our Sages]" -- find which statement of our Sages he is referring to, and you'll probably find more information.
–
MenachemApr 26 '13 at 2:19

From Rabbi Chaim Kaner Family First magazine 24,4,13
The earliest source for not skipping an older child stems from a comment of the rashbam in BB 120a. Tlofchod had five daughters and married according to age. Like Lavan said the older comes first.
Rav Graubart, in 'chavalim banimim' that yaakov didnt agree with lavan.
The Maharsham 3:136 says its a matter of courtesy not halacha. Therefore since a boy has mitsva to marry and not a girl he may go ahead. Also if the older sibling is 27 or more the younger need not wait. The sefer Shulchan hoezer is stringent in these matters. Since he is shaming his older sibling even a boy cannot marry before a girls. Shaming a person takes precedence over the mitsva. RMF says one doesnt have to wait only for the wedding not the engagement. RMF does not consider it to be shaming.
This is in short the article.